Update sphinx requirement from <7 to <8

Updates the requirements on [sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v0.1.61611...v7.3.7)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

setup.py

@@ -35,7 +35,7 @@
 docs_requires = [
     "furo",
     "myst-parser[linkify]>=0.18,<4",
-    "sphinx<7",
+    "sphinx<8",
     "sphinx-copybutton",
     "sphinx-design-elements<1",
     "sphinxcontrib-mermaid<1",